1. Field of the Invention
This invention relates to a novel and excellent light-sensitive film.
2. Description of the Prior Art
As amorphous semiconductor materials for photoconductive materials, there have heretofore been known a material containing a group-IV element such as Si and Ge as its main constituent, a material containing a group-V element such as As as its main constituent, and a material containing a group-VI element such as Se and Te as its main constituent. Among them, the latter two materials often employed at present are toxic substances. Therefore, the amorphous materials whose main constituents are Si, Ge etc. free of toxicity are desired.
Recently, the amorphous body of silicon (Si) containing hydrogen (H), the amorphous body of germanium (Ge) containing hydrogen, and an amorphous material corresponding to an alloy thereof have been deemed hopeful as materials for electron devices. For example, the amorphous silicon and germanium containing hydrogen have been reported by J. Chevallier et al in `Solid State Communications`, vol. 24, pp. 867-869, 1977. These materials, however, are of a limited number and set limits to characteristics in case of considering wide applications as the materials for electron devices. By way of example, the band gap (E.sub.g) which is the most important factor for determining the characteristics of an electronic material can be selected only within a range of 0.8-1.65 eV when the Si- and Ge-based amorphous materials are resorted to.
An important example of application of the photoconductive material is a light-receiving face for photoelectric conversion. In case of applying conventional photoconductive materials to light-sensitive films which are used in the storage mode, there have been problems to be stated below.
An important characteristic requested for a photoconductive layer is that a charge pattern stored in the photoconductive layer does not vanish due to diffusion within a time interval in which a specified picture element is scanned for photoelectric conversion by an electron beam or the like (that is, within a storage time). Accordingly, semiconductor materials whose resistivities are at least 10.sup.10 .OMEGA..cm, for example, Sb.sub.2 S.sub.3 -, PbO- and Se-based chalcogenide glasses are usually employed for the photoconductive layer. In case of employing a material such as Si single crystal whose resistivity is less than 10.sup.10 .OMEGA..cm, the surface of the photoconductive layer on the electron beam scanning side needs to be divided in a mosaic pattern so as to prevent the decay of the charge pattern. Among these materials, the Si single crystal requires a complicated working process. The other semiconductors of high resistivities are inferior in the photo response characteristics because they ordinarily contain at high densities the trap levels which impede the transit of photo-carriers, and an imaging device is liable to the drawback that a long lag or an after-image occurs.